Such bending apparatus are used in modern bending machines for rod-like workpieces and for prefabricated conduits primarily having larger cross sections.
In such cases the bending apparatus constitutes a plurality of units whose interaction makes good bending results possible, especially in the case of tubular workpieces with thin walls.
A bending apparatus should ideally be able to satisfy a majority of particular requirements in that it should be able to perform the following functions: right-hand and left-hand bending, draw bending and curling, coiling, producing a bend directly after a different bend without an intervening straight segment, producing bends with different radii, bending pipes of different diameters, preventing wrinkling, three-dimensional bending, and enabling simple retooling.
Bending devices are known with bending heads that must be e.g. pivoted to convert from left to right coiling (see EP 1 226 887 B1, EP 1 291 094 B1 and EP 1 350 578 A1), or which are constructed symmetrically (WO 03/053 606 A1). Likewise, the possibility of exchanging a bending head for such a conversion is also known.
Also prior art is the use of multi-stage dies for producing different bending radii and for processing workpieces of different diameters, as well as the use of forming jaws for producing sequential bends without an intervening straight segment (see EP 1 350 578 A1 and WO 03/053 606 A1). The use of a slide rail to support and track the material is also known (see EP 1 291 094, EP 0 963 800 B1 und U.S. Pat. No. 6,651,475).
WO 2004/000479 A1 describes a bending apparatus of the type named at the beginning that can be used both for left-hand and for right-hand bending, without the bending mandrel having to be changed. It is essentially circular in design and has two circular forming grooves arranged on it that are axially offset from one another, one of which is used for left-hand bending and the other for right-hand bending. However, positioned on each of the forming grooves, at the place where the free end of the bent pipe again emerges tangentially from the ring groove when bending pipe, is a corresponding forming piece that itself has a straight-line forming segment that branches off tangentially from the corresponding forming groove, so that an end piece of the pipe to be bent that diverges in a straight line tangentially from the bend lies in this section of the forming groove. For bending, the pipe delivered by a feed device is placed and pressed against the corresponding forming groove section of the forming piece that diverges tangentially from the forming groove in question, by means of a clamping device that can be moved relative to the bending mandrel, after which, when the pipe is clamped in place, the clamping device is pivoted together with the bending mandrel concentrically to the rotational axis of the latter, until behind the straight-line section of the forming groove, in the adjacent ring groove, the pipe is bent accordingly during the rotation. The clamping device is then separated from the bending mandrel, and the bent area of the bent pipe is removed from the forming groove of the bending mandrel and its straight-running end area is removed from the forming groove section of the forming piece.
If the same pipe is then to receive e.g. another bend in the other direction, which is to be e.g. directly adjacent to the first bend, the piece of pipe that has already been bent is moved to the other side of the bending mandrel, to the elevation of the other forming groove on the bending mandrel. At the same time, the clamping device is pivoted about the rotational axis of the bending mandrel relative to the latter so that it is positioned on the other side of the mandrel, and the pipe is again present between it and the bending mandrel. The pipe is then re-clamped between the clamping device and the bending mandrel (there again in a forming piece mounted correspondingly on the other forming groove, having a segment of forming groove that runs in a straight line, emerging tangentially from the forming groove of the bending mandrel), and the new bend in the pipe is then produced by rotating both the clamping device and the bending mandrel about the rotational axis of the bending mandrel, this time in the opposite direction.
Since there are two forming grooves on the bending mandrel, axially offset to one another, for left-hand and right-hand bending, each of which has an associated fitting with the straight-line segment of forming groove, and since (because of the difference in bending direction) the two fittings protrude linearly from the bending mandrel in opposite directions, albeit by different amounts, accordingly the clamping device, since in each of its pivoted positions for the two bending directions it must cooperate with one of the forming grooves and the associated forming segment at different heights, must also have forming grooves positioned corresponding to the difference in level to press the pipe against the bending mandrel and its forming segments. This requires geometrically that the corresponding forming grooves, as well as the fittings on the bending mandrel, must also be adjacent to one another, which results in a complicated structure and a relatively great width of the clamping device, but which is not favorable in view of the desired compact construction of such bending devices. The same is also true of the wrinkle smoother utilized there in the form of relatively long guide strips immediately upstream of the clamping device in the feeding direction of the pipe, with a corresponding forming groove for placing the wire. Here too, because of the difference in height of the forming grooves on the bending mandrel with respect to left-hand and right-hand bending, two different smoothing strips must be used that point in opposite directions, where each embodies a forming groove, and that must also be moved by corresponding travel distances next to the sliding mandrel. This too takes up more space than desired. The publication says nothing about how the movement of the clamping device relative to the bending mandrel is realized, but it can be seen from the illustrative figures in the publication that a shifting occurs along a guide strip that is mounted on the underside of the clamping device and is overlapped and positively gripped by the latter, for which it is quite obvious that a linear drive must be used, although this is not described in further detail there.
Starting from this basis, the object of the invention is now to improve such a bending device such that the clamping device gets by with an especially small space requirement and a separate linear positioning motor is not needed for the linear movement of the clamping device.